I've used AVG free on all my systems (4-8 of them) for years now and no problems. Ironically I've found it even more reliable than many of the commercial apps at times (e.g. a friend will send me a file and I'll find a virus in it and they'll tell me their own virus scanner found nothing - these are not false positives either). It's also reasonably low in resource use. I just got Vista myself and was glad to find AVG already compatible with it. So I've got it installed and it's doing fine so far. Above all I would recommend *against* any Norton or Mcaffee product for paid A/V. If you want to pay I'd say PC Cillin, Kaspersky, NOD32, or CA/ETrust are good.
- Oshyan